(1) Field of the Invention
This invention relates to polymeric electrodes. More particularly, this invention relates to negative electrodes for non-aqueous secondary batteries composed of conjugated backbone polymers and alkali metals which are plated on or distributed throughout the polymer matrix.
(2) Prior Art
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene, polyacenes, polythiophene, poly(phenylene vinylene), polyazulene, poly(phenylene sulfide), poly(phenylene oxide), polythianthrene, poly(phenylquinoline), polyaniline, poly(N-methyl-carbazole), and polypyrrole, have been suggested for use in a variety of applications based upon their characteristic of becoming conductive when oxidized or reduced either chemically or electrochemically. The secondary battery application described by, e.g., MacDiarmid et al. in U.S. Pat. No. 4,442,187 (1984); J. de Physique, Colloque C3, Vol. 44 (1983), articles beginning on page 579, page 615 and page 537; and K. Kaneto et al., Japanese J. of Applied Physics, Vol. 22, pp. L567-L568 (September 1983) and pp. L412-L414 (July 1983), employs one or more electrodes having conjugated backbone polymers as the electroactive material. Such electrodes can, for example, be electrochemically n-doped by reversible insertion of alkali metal cations or tetraalkylammonium cations during battery cycling, most commonly with insertion of cations into a polymer anode (the negative battery electrode) occurring during charging. The more such cations are inserted, the more conductive the electrode becomes and the more cathodic the potential of the anode becomes. This electrochemical doping process is described by MacDiarmid et al. in U.S. Pat. No. 4,321,114 (1982).
Lithium and lithium alloys have been suggested for use as the negative electrode in electrochemical cells. For example, U.S. Pat. No. 4,002,492 discloses electrochemical cells having an anode consisting essentially of lithium aluminum alloys that contain lithium in amounts between about 63% and 92% and the balance essentially aluminum. Anodes composed of lithium and aluminum are also disclosed in Rao, et al., J. Electrochem. Soc. 124, 1490 (1977), And Besenhard, J. Electroanal. Chem., 94, 77 (1978).
An application of Matsushita (kokai 58-163184) discloses the use of electroconductive polymer as a covering at the surface of the electrode to protect against short circuiting because of dendrite growth.
European Pat. No. 0070107 Al; Murphy et al., J. Electrochem. Soc., 126, 349 (1979) and Murphy et al., Mat. res. Bull., 13, 1395 (1978) disclose batteries based on lithium intercalation in layered dichalcogenides for use as cathodes.
Composite structures of a conjugated backbone polymer and a non-electroactive material have been described in U.S. Pat. No. 4,294,304 and in the above J. de Physique issue, articles beginning on page 137 and on page 151. Representative other components that have been blended with polyacetylene or onto which polyacetylene or polypyrrole have been deposited include polyethylene, polystyrene, graphite, carbon black, NESA glass and silicon. In selected instances, such composite structures have been suggested for use in batteries, see Showa Denko K. K., European Published Patent Application No. 76,119 (1982).
While batteries have heretofore been constructed in which a conjugated backbone polymer comprises the largest part of the electroactive material, such batteries suffer from a number of disadvantages. For example, such cells have heretofore exhibited strongly varying discharge potentials. Moreover, such cells have relatively low volumetric energy densities.
Batteries to be used at room temperature which are constructed with anodes composed of lithium or lithium alloys such as lithium/aluminum alloys, also suffer from a number of disadvantages. While lithium is inherently rechargeable, it's practical rechargeability is poor because at practical current densities metallic lithium is electrodeposited in the form of dendrites which can eventually lead to shorting out of the cell. High discharge rates can also result in irreverible shape changes in the electrode. In order to minimize the effects of dendritic growth, it has been suggested to employ cell separators, such as permeable membranes or the composite of Kokai 58-163184, which act as physical barriers to dendritic growth. Although these solutions are initially effective, eventually the lithium dendrites may penetrate the barriers and establish transient of permanent electronic shorts. It has been suggested that use of alloys of lithium with a less reactive metal, as for example, alloys of lithium and aluminum obviate certain of the disadvantages attendant to the use of lithium as the anodic material. See for example, U.S. Pat. No. 4,002,492. However, such batteries have exhibited relatively low capacities (utilization), low rate capabilities and poor cycle lifes.